Zinc dithiophosphates

ABSTRACT

ANTI-OXIDANTS ARE DISCLOSED HAVING THE FORMULA:   R-O-P(-O-R&#39;&#39;)(=S)-S-M-S-P(=S)(-O-R&#34;)-O-R&#34;&#39;&#39;   WHEREIN M IS CALCIUM, BARIUM, NICKEL, CADMIUM, LEAD OR ZINC AND R, R&#39;&#39;, R&#34; AND R&#34;&#39;&#39; ARE SUBSTITUTED OR UNSUBSTITUTED HYDROCARBON RADICALS, AT LEAST ONE HAVING THE FORMULA:   (2-R2,3-R1,4-R3,5-R4,5-R5-PHENYL)-(A)N-   WHEREIN A IS A BIVALENT HYDROCARBON RADICAL AND N IS ZERO OR A WHOLE NUMBER FROM 1 TO 20 AND AT LEAST ONE OF SAID R1, R2, R3, R4 AND R5 GROUPS IS A HYDROXY GROUP STERICALLY HINDERED BY ANOTHER OF SAID GROUPS WHICH IS AN ALKYL GROUP. THE REMAINING GROUPS ARE HYDROGEN OR ALKYL.

United States Patent US. Cl. 260-4299 6 Claims ABSTRACT OF THE DISCLOSURE Anti-oxidants are disclosed having the formula:

R0 OR" RO OR wherein M is calcium, barium, nickel, cadmium, lead or zinc and R, R, R" and R are substituted or unsubstituted hydrocarbon radicals, at least one having the formula:

a B4 Rs wherein A is a bivalent hydrocarbon radical and n is zero or a whole number from 1 to 20 and at least one of said R R R R and R groups is a hydroxy group sterically hindered by another of said groups which is an alkyl group. The remaining groups are hydrogen or alkyl.

This invention relates to novel compounds which are suitable as anti-oxidant additives for lubricants, and to lubricants containing these compounds.

It is known that zinc dialkyldithiophosphates are used as additives for lubricating oils on account of the fact that these compounds impart to the lubricants to which they are added a strong resistance against oxidation, as well as anti wear and anti-corrosion properties.

It is also known that sterically hindered phenol compounds, for example 2,6-di-t.-butylparacresol, are commonly employed as anti-oxidant additives. In addition, it is known that some mixtures of zinc dialkyldithiophosphates and sterically hindered phenols, impart to the lubricant a high resistance to oxidation because of the synergism existing between those two classes of additives.

According to the present invention, there is provided as an anti-oxidant additive for a lubricating oil a compound represented by the following general formula:

RIO OR!!! wherein M is a calcium, barium, nickel, cadmium, lead or zinc atom, and R, R, R" and R' are substituted or unsubstituted hydrocarbon radicals, at least one of R, R, R

and R' having the following general formula:

where A is non-existent or is a bivalent hydrocarbon radical containing from 1 to carbon atoms and optionally containing an ether, ester or thioether group, at least one of the radicals R R R R and R isa hydroxyl group,

Patented Apr. 4, 1972 at least one other of the radicals R R R R and R is an alkyl group which sterically hinders the said hydroxyl group, and each of the remainder of the radicals R R R R and R is a primary, secondary or tertiary alkyl group or a hydrogen atom.

Preferably A is a bivalent hydrocarbon radical containing from 2 to 10 carbon atoms. Advantageously, the alkyl radical which sterically hinders the hydroxyl group is a secondary or tertiary alkyl group.

Preferably, there are two alkyl radicals having a steric hindrance on the hydroxyl, which are in a vicinal position with respect to the hydroxyl. Examples of suitable radicals for this purpose include t.-butyl, dirnethyl-ethyl-methyl, methyldiethylmethyl, triethylmethyl, isopropyl and sbutyl. The products of this invention possess approximately the anti wear and anti-corrosion properties found in the zinc dithiophosphates obtained from n-alcohols.

The metal dithiophosphates of the invention may be obtained by reacting P 5 and the appropriate alcohol or alcohols in the approximate molar ratio of 1:4, at an elevated temperature, generally at a temperature of from 50 C. to 200 C., preferably from C. to 120 C., and then neutralizing the resulting dithiophosphate acid with a metallic oxide, for example zinc oxide.

The invention will now be illustrated by the following examples.

EXAMPLE 1 Preparation of bis [(3,5-di-tert.-butyl-,4-hydroxy-benzyl) propyl] zinc dithiophosphate 0.4 mole (3,S-di-tert.butyl-,4-hydroxy-benzyl)-propanol were reacted with 0.1 mole of P 8 suspended in benzene at the boiling point of benzene. The reaction was over after about an hour. The benzene was filtered and distilled off under reduced pressure. The resulting dithiophosphoric acid was heated with ZnO in the presence of an inert solvent which forms an azeotrope with water, in this case toluene, in order to neutralize the product. Then the inert solvent was evaporated off and a solid, resinous, orange yellow coloured product was obtained in a yield of Analysis of the product gave the following results:

Calculated (percent): P, 4.73; Zn, 4.99; S, 9.80. Found (percent): P, 4.6; Zn, 4.8; S, 9.9.

Infrared spectrographic analysis confirmed the presence of a dithiophosphate group.

EXAMPLE 2 Preparation of 4-methyl-2-pentyl) [(3,5-di-tert.butyl- 4-hydroxy-benzyl)-propyl] zinc dithiophosphate A mixture of 0.2 mole (3,5-di-tert.butyl-4-hydroxybenzyl)-propanol and 0.2 mole 4-methyl-2-pentanol were allowed to react with 0.1 mole of P 8 under the same conditions as in Example 1, and the product was similarly neutralized with Z to form a liquid, viscous, brownorange coloured product in a yield of 97%.

Analysis of the final product gave the following results:

Calculated (percent): P, 6.29; Zn, 6.63; S, 13.02. Found (percent): P, 6.3; Zn, 6.3; S, 13.3.

Infrared spectrographic analysis confirmed the presence of a dithiophosphate group.

EXAMPLE 3 Preparation of the cetyl [(3,5-di-tert.butyl-4-hydroxylbenzyl)-propyl] zinc dithiophosphate A mixture of 0.1 mole of (3,5-di-tert.butyl-4-hydroxybenzyl)-propanol and of 0.3 mole cetyl alcohol was allowed to react with 0.1 mole of P 5 in a manner similar to that described in Example 1. After neutralization with zinc oxide, a solid, waxy yellow orange coloured product was obtained in a yield of 96%.

Analysis of this product gave the following results:

Calculated (percent): P, 4.98; Zn, 5.25; S, 10.31. Found (percent): P, 4.8; Zn, 5.1; S, 10.4.

The infrared spectrographic analysis of the product confirmed the presence of a dithiophosphate group.

EXAMPLE 4 Evaluation of the anti-oxidant properties The Staeger oxidation test was carried out on a SAE 30 parafiinic mineral oil with a high viscosity index containing the products of this invention or other additives and the results are shown in the following Table 1.

From Table 2, it can be seen that the additives of the invention have anti-wear characteristics of a similar nature The test consisted in heating in a thermostatic stove maintained at 110 C. the oil containing the additives to known addmves' under examination. A strip of electrolytic copper was EXAMPLE 6 immersed in the oil to act as an oxidation catalyst. At Amirust test regular intervals the variation 1n the neutralization number, based on the weight in mg. of KOH./g. oil was 2 In the following Table 3 there are reported the results recorded. found in tests on the anti-rust characteristics of oils con- The test was considered completed when there wa an taining the same additives as Table 2. The tests were carincrement of 0.25 in the neutralization number. Oxidaried out according to the method ASTM/ D 665-54. tion tests were also carried out at 150 C. in the same way as those at 110 C. The concentration of the addi- TABLE 3 tives according to the invention was constant in each Concen- Base oil, case. The content of phosphorus was 44. 10 g. percent, Additive ggf gg si- 1 Rust grade correspondmg to 0.7 millrmole of dlthiophosphate per kg. of solution. The comparative additives were selected 8'82 32 gg from zinc dithiophosphates obtained from aliphatic 0:03 2: Do: alcohols and mixtures thereof with 2,6-di-tert.butyl-para- 8'83 i h g' cresol in equimolar concentrations based on the additives 0:03 2:95 Slight. of the invention.

TABLE 1 Oxidation Oxidation (hours at (hours at 150 necessary to necessary to have an have an Cone. increase of the increase of the (m. mole/ neutralization neutralization kg. of number of number of Additive in SAE 30 mineral oil solution) 0.25) 0.25)

None. 310 Zn bisbutyldithiophosphate 0. 7 810 Bis 1 methyl-2-pentyl) Zn dithiophosphate, 0. 7 1, 120 BiS-cctyl Zn dithiophosphate 0. 7 820 Bis-butyl Zn dithiophosphate 0. 7 1,350 250 2,6di-tert.butyl paracresol 2. 8 Bis[(3,5-di-tert.butyl-,4-hydroxybenzy1)- propyllZn dithiophosphate 0. 7 1, 610 370 Bis(4-methyl-2-pentyl)Zn dithiophosphatc. 0. 7 1, 260 210 2,fi-di-tert.butylparacresol 1, 4 (4-methyl-2-pentyl)-[(3,5-di-tcrt.butyl-,4-

hydroxy-benzyl)-propyl]Zn dithiophosphate 0. 7 l, 420 230 Bis-cetyl Zn dithiophosphate 0. 7 l, 250 270 2,6-di-tert.butylparaercsol O, 7 cetyl [(3,5-di-tert.butyl-4-hydroxybenzyl)- plopyllZn dithiophosphate 0. 7 1,320 300 As can be seen from the oxidation tests recorded in Table 1, the zinc dithiophosphates of the invention have a high anti-oxidant activity, and the synergism existing between the dialkyl zinc dithiophosphates and sterically hindered phenols, increases when the sterically hindered phenol forms part of the dithiophosphate molecule.

EXAMPLE 5 Anti-wear tests In the following Table 2, there are shown the results found in tests in tests on the anti-wear characteristics of an oil containing the products of this invention, compared with the same oil containing known commercial additives.

In Table 2, A is the additive of the Example 1, B the additive of the Example 2, C the additive of the EX- ample 3 and D, E and F are different known commercial additives based on Zinc dithiophosphates. The tests were carried out with a Shell 4 ball Wear Tester, each test lasting 60 seconds at a speed of 1200 r.p.m.

Thus, as can be seen, the additives of the invention generally have a better anti-rust characteristic than known additives.

What we claim is:

1. A compound represented by the following formula:

RIO

wherein M is a calcium, barium, nickel, cadmium, lead or zinc atom; and R, R, R" and R' are alkyl radicals containing up to 10 carbons, at least one of R, R, R" and R having the formula:

2. A compound as claimed in claim 1 wherein said hydroxy group is sterically hindered by vicinally positioned secondary or tertiary alkyl groups.

3. A compound as claimed in claim 1 wherein said hydroxy group is in the para position sterically hindered by vicinally positioned tertiary butyl groups.

4. A compound as claimed in claim 1 having the name bis[( 3,5 di-tert.butyl-4-hydroxy-benzy1)propyl] zinc dithiophosphate.

5. A compound as claimed in claim 1 having the name (4 methyl -2- pentyl) [(3,S-di-tert.butyl-4-hydroxy-benzyl)-propyl] zinc dithiophosphate.

6. A compound as claimed in claim 1 having the name cetyl[(3,5 di tert.buty1-4-hydroxy-benzyl)-propyl] zinc dithiophosphate.

References Cited UNITED STATES PATENTS Rutherford et al. 25235 Cook et a1 260448 X Reifi et a1. 25232.7 Welsh 25232.7 Arakelian 260429.9 Miller 260429.9 Goldsmith 260429.9 X

TOBIAS E. LEVOW, Primary Examiner H. M. S. S NEED, Assistant Examiner US Cl. X.R. 

